A Christian counselling ministry is urging the government not to go ahead with its planned conversion therapy ban after a major report said it should cover religious practices including "spoken prayer".
The Cooper Report also says there should be no exemptions for "consenting adults" or prayers for the "healing" of same-sex attracted people.
The report was commissioned by the Jayne Ozanne Foundation and is supported by a number of parliamentarians and lawyers.
It claims that an exemption for "religious conversion practices" like "an act of spoken prayer directed at an individual with the predetermined purpose of suppressing, curing or changing their sexual orientation or gender identity, would undermine the efficacy of the prohibition".
"For the same reason, there can be no exemptions for 'consenting' adults who seek out conversion practices despite the harm involved," it continues.
"This is because the pressures and imbalance of power involved mean that such 'consent' cannot be truly free or autonomously exercised. Allowing these to continue would put a significant number of vulnerable people at risk."
Elsewhere, the report states "that even so-called non-coercive forms of conversion practices such as talking therapy or 'healing' prayer, which are seen by some as 'soft' forms of conversion practices, still amount to degrading treatment due to the actual harm or the real risk of grave psychological harm to which they expose their victims".
Writing in the foreward to the report, Baroness Kennedy QC, Chair of the International Bar Association's Human Rights Institute, said so-called conversion therapy practices were "degrading and inhumane", and "must be criminalised in all their forms".
"I and my co-signatories propose that the most effective way of doing this is through a two-pronged approach that utilises both the criminal and civil law," she said.
"This then protects those who are immediately vulnerable and at risk, whilst also making it clear in law to would-be perpetrators that their vile practices will not be tolerated in a civilised society."
She adds, "Together we urge the government to implement their promised legislation without delay, ensuring that there are no loopholes – too many lives have already been impacted by this horrific abuse and countless more are still at risk."
The ban is being challenged by a number of Christian groups who fear for the freedoms of pastors and churches.
Mike Davidson, of Christian counselling charity Core Issues Trust, says that people must be free to seek help with unwanted same-sex attraction.
He said the Cooper Report "adds nothing new" to the debate and is urging the government to uphold therapeutic choice.
"Instead of citing new empirical findings conclusively proving harms the report makes endless claims to authorities that support its own ideology," he said.
"Only one viewpoint is represented and once again there are no contrary voices from those who disagree or whose personal experience has been different. Former LGBT-identified persons are redacted from the social record.
"It's time to recognise calls for bans on conversion practices for what they are: the beginning of the end of the freedom of the Gospel, and the fruit of delusion of those who have believed a lie and worshipped the creature rather than the Creator and so forfeited the nation's righteousness.
"Countless individuals know that we don't have to be victims of our sexual feelings or gender confusions and that transformation is a reality for those who choose a different pathway."
He added, "Denying therapeutic and counselling choice to those seeking it is untenable. The government knows it but will it do the necessary work to protect the rights and freedoms of former LGBT persons equally protected under the Equality Act who continue to be marginalised in our country?"
The UK Evangelical Alliance has warned Prime Minister Boris Johnson that the ban poses a "direct threat to religious liberty" and leaves ministry leaders at risk of arrest.
"Proposals, as currently discussed, could have the consequence of restricting individual freedom and impinging on essential religious liberty - potentially criminalising Christians and common church activities," EA UK director Peter Lynas has said.
"We are deeply concerned at some of the practices that have been carried out which are categorised as conversion therapy, but also by the government's lack of clarity on the issue."
The Christian Institute has warned that the ban "risks criminalising the ordinary work of churches".